Elasticsearch is often deployed as a cluster of nodes. A variety of APIs let you
manage and monitor the cluster itself, rather than interact with the data stored
within the cluster.

As with most functionality in Elasticsearch, there is an overarching design goal
that tasks should be performed through an API rather than by modifying static
configuration files. This becomes especially important as your cluster scales.
Even with a provisioning system (such as Puppet, Chef, and Ansible), a single
HTTP API call is often simpler than pushing new configurations to hundreds of
physical machines.

To that end, this chapter presents the various APIs that allow you to
dynamically tweak, tune, and configure your cluster. It also covers a host of
APIs that provide statistics about the cluster itself so you can monitor for
health and performance.